Saswata Chatterjee who plays the evil villain Bob went to see the film with his wife where in his wife would close her eyes whenever he appeared on screen because he was too evil in the film.
Nawazuddin Siddiqui got a major breakthrough with this film as he struggled for 12 years in just small character roles. After Kahaani he became one of the busiest actors.
Popular Hindi actors were not willing to work with him Sujoy Ghosh after his two flops. He also believed that audience might expect more screen-time from a better-known actor. Hence he cast more Bengali actors in the film who were lesser known in Hindi films.
Though in the film the cellphone proves to be a tool for Bob Biswas as his prospective victim's photo is sent to him via MMS, in real life Saswata Chatterjee (who portrayed Bob Biswas )doesn't even use a mobile and has only a landline number as a point of contact.